Details

The popularity of the Dahlia continues to increase. The reasons for this devotion are fairly obvious. First of all the skill of the breeders in England, Holland, Germany, Australia and America have produced a range of sizes and colours unmatched in the world of garden flowers.
Equally important is the time of flowering. From the end of July to the first frosts, Dahlias provide large orbs of colour when so many flowers are past their best. Above all the Dahlia is an accommodating plant. It likes a good loam, but will grow almost anywhere. It relishes sunshine, but can still do well in partial shade.

Dahlia variabilis 'Decorative Giants' produces a range of large flowered, long stemmed blooms in an eclectic mix of both colours and forms.
Some flowers are single, while others are semi-double or fully double. Others have quilled or curved petals, elegantly rolled with pointed tips. The long stems grow 120 to 150cm (45 to 60in) tall.
With a range of the most electric colours in the garden, they are ideal for making a splash of colour in the border or in the vase throughout the summer months.

Dahlias are straightforward to grow from seed. They will flower twelve weeks from sowing until first frosts.
Superb as a cut flower and excellent for creating a statement in displays and herbaceous borders. They are particularly useful for filling in gaps that appear as other plants go to seed.
Seed-raised Dahlias flower well especially towards the autumn. They are generally treated as annuals though they produce a tuber to survive the winter, which can be dug up, stored and replanted the following year.

Sowing: Sow in spring for flowers 12 weeks from sowing.
Fill cells or pots with a free-draining, seed sowing compost, and stand in water so that the compost is thoroughly damp, then allow to drain. It is advisable at this point to use a suitable fungicide prior to sowing, to prevent damping-off disease (available from any garden centre)
Sow the seeds onto the surface of the compost and cover with a layer of vermiculite. Cover the trays with clear or milky polythene to maintain humidity, until the first seedlings are visible. Keep moist at all times.
Germination takes around 7 days at 18 to 20°C (65 to 68°F)

Transplanting:
Once germination takes place, remove the cover and keep the seedlings moist.
As soon as the plants are large enough to handle, usually at around three weeks, prick out into 7cm (3in) pots to grow on at 15 to 18°C (59 to 65°F).
Harden off and plant outdoors 30 to 45cm (12-18in) apart in soil with a good nutrient content.
Once the plants are established, a balanced liquid feed can be applied to promote flowering.
Take prevention against slugs – they love Dahlia seedlings!

Cultivation:
Water well in summer, Dahlia do not like dry conditions. Feed weekly during the growing season and dead head regularly. Plants are sturdy but may need some support in exposed situations.
Cut flowers early or late in the day when the blooms are almost fully open.

Overwintering:
When the foliage begins to die back, cut stems to 15cm (6in) and lift the tubers. Store in straw, wood shavings, or vermiculite in a frost-free place. Divide tubers in spring and plant out once danger of frost has passed. The soil temperature should be at least 13°C (55°F). If planted before this temperature is reached may rot before they can sprout.

Nomenclature:

Native to Central America, the genus Dahlia was named in honour of Anders Dahl (1751-1789), an 18th century Swedish botanist. He was a pupil of Linnaeus. (the man responsible for the binomial system of naming plants, where the genus is followed by the species.)
Andreas Dahl regarded it as a vegetable rather than a garden flower, but interest switched from the edible tubers to the blooms when the first varieties with large, double flowers were bred in Belgium in 1815.
Although dahlias were discovered in the 16th century by Spanish conquistadors, not until 1872 was a box of tubers sent to Holland. Within a few years nearly every colour we now admire had been introduced and Victorian catalogues listed hundreds of varieties.
From just a handful of original species Dahlias have been hybridised over the centuries into an amazingly diversified genus, with plant sizes from 30cm to 200cm (1 to 7ft) tall, and flowers in almost any colour imaginable from 5cm to 30cm (2 to 12in) wide.